Pressure sensitive adhesives are widely employed on tapes, labels, carpet tiles and many other articles commonly employed in the home, offices and factories. On many of these articles the adhesive surface is protected by a release "paper" which may be easily peeled off immediately prior to use.
It should be understood that as used herein, the term release "paper" is used to include not only paper but also other protective substrates such as synthetic films, e.g. polyethylene, pvc, polyester, etc., which require release properties when employed as a protective backing on adhesive surfaces. Also, it is possible to coat the adhesive directly over the cured solventless silicone composition and thereafter employ a transfer coating technique to place that adhesive against the appropriate face stock surface.
The release "papers" of the prior art have been coated with silicone compositions that have been applied in a solvent or emulsion type of dispersion. This coating method has required a curing cycle which would effect removal of any solvent or extraneous liquid that was present in the silicone containing dispersion. The presence of these extraneous liquids required higher energy costs for drying and also pollution problems were caused by the need to vent the solvent. Also, if the solvent was collected and recycled, this further added to the cost. Recently, solvents have been in short supply and this has also contributed to production problems.
Therefore, a need has existed for a process that could efficiently produce a release "paper" without the use of a solvent. One problem encountered in the direct application of a solvent-free silicone fluid is the difficulty in controlling the amount of silicone fluid that is applied to the "paper" substrate so that a minimum effective amount of silicone may be applied. This minimum amount is important for producing an acceptable release "paper" at economic application rates.
Conventional offest gravure coating techniques have not been satisfactory for this purpose as the application levels have been too high to be acceptable. It has been discovered that the application level may be reduced to acceptable levels if the substrates is run through the gravure coating apparatus at a linear speed that is greater than the linear speed of the gravure roll.
Accordingly, it is a primary object of this invention to provide a method of manufacturing a release "paper" which is carried out without the aid of a solvent or emulsified system.
It is also an object of this invention to provide a method for coating a substrate with a minimum effective amount of a silicone composition.
It is also an object of this invention to provide a method of making a release "paper" with a minimum use of energy and a minimum amount of pollution of the environment.